Cursor position is incorrect when using CJK characters

What version of Codex is running?

0.36.0

Which model were you using?

gpt-5-codex

What platform is your computer?

Darwin 24.6.0 arm64 arm

What steps can reproduce the bug?

Input any Chinese, Japanese, or Korean (CJK) characters into the terminal. For example, you can type or paste the following characters: "文文文文"

What is the expected behavior?

The cursor should be positioned immediately after the last entered character, accurately reflecting the end of the input string.

What do you see instead?

<img width="519" height="310" alt="Image" src="https://github.com/user-attachments/assets/a6ba07d7-fac7-4cd3-9a37-730b6bc61729" />

The cursor is positioned incorrectly, appearing several spaces after the last character. The offset increases with the number of CJK characters entered.

Additional information

_No response_